1. Field of the Invention
The present invention relates to an apparatus and a method for sharpening an edge of a blurred enlarged image, that can be applicable even to a high definition digital image of more than 2 k (horizontal resolution of 2000 pixels in an image), and more particularly, to an apparatus and a method for sharpening a blurred enlarged image by performing high-pass filtering the edge of an enlarged digital image adaptively without ringing or artifact to obtain a sharp image using a digital image processing technique.
2. Description of the Related Art
The present invention has been derived from a research conducted as a part of information technology (IT) new growth power core technology development business by Ministry of Information and Communication, Republic of Korea, and Institute for Information Technology Advancement (Project management No.: 2005-S-003-02, Project title: real-picture level digital image contents producing software).
For methods for sharpening an edge in a still image or a moving image, there are many Korea patent applications including Korea patent application Nos. 10-2003-0069837 and 10-2002-7003343. In the methods for sharpening an edge proposed by the above Korea patent applications, it is judged using a predetermined critical value set in advance whether to perform sharpening on an edge region. In the case where a user performs the edge sharpening with the set critical value, a sharpening-performed portion is not smoothly connected with a sharpening-not-performed portion, so that not only distortion is easily detected on an enlarged image, but also a ringing or artifact generated due to side effects during the edge sharpening still exists.
To solve this limitation, Korea patent application No. 10-2004-0094267 uses a finite impulse response (FIR) digital filter to obtain an enlarged image having a sharp edge without distortion. When this digital filter is used, an edge can be sharpened without a ringing or artifact.
However, in the case where the FIR digital filter proposed by the above-mentioned Korea patent application is used, image blurring is still generated when an image is enlarged from resolution of 1024×768 to resolution of 2048×1556 using an enlarging ratio of twice or more. Therefore, when the edge sharpening of an enlarge image is performed using the digital filter, a sharp image that is so sharp as to be used for high definition (HD) digital image media cannot be obtained.
As the size of an enlarged image increases, the blurring of the enlarged image gets serious even more. When the edge sharpening is performed to remove the blurring, a ringing or artifact appears conspicuous. Accordingly, the general edge sharpening methods proposed by the above-described Korea patent applications may not be suited for a HD digital image of 2 k or more.